This invention relates to linear motors and, in particular, to what are known as voice coil linear motors due to the similarity to the voice coil mechanism in permanent magnet acoustic speakers.
In the prior art, voice coil motors or actuators have been used in a variety of applications, eg. magnetic head positioners in disc or tape drives, valve actuators, sonar transducers, vibration test equipment, and deflection mirrors for laser scanners. These applications typically require simply a short thrust of moderate force to accomplish the desired result.
In the manufacture of semiconductor devices, there is increasing emphasis on increasing the degree of automation and increasing the rate at which product is manufactured. Semiconductor devices are manufactured from silicon wafers, or other semiconductive material, approximately twenty mils (one half millimeter) thick, or less. Silicon is a brittle material and will crack if not handled carefully. The silicon wafer is diced or divided into chips or die which represent almost complete devices. The die must still be assembled into packages or carriers to obtain functional devices.
Because of the delicateness of silicon, or other semiconductive materials, the automatic handling of the die requires careful control of the forces applied to the die. One example of a manufacturing step where this occurs is in the die bond operation, where a die (the same word is used as either singular or plural) is removed from the wafer and placed on a header, eg. a metal member such as a lead frame, to which the die is soldered, brazed, or otherwise attached.
The desire for increased speed in manufacturing imposes the contradictory requirements of higher speed and not subjecting the die to excessive force. A voice coil motor can be cycled at the desired speed, if the moving parts are sufficiently light. However, merely designing a light bobbin does not necessarily solve the problem of not subjecting the die to excessive force.
Another problem in automated equipment is knowing where the moving parts are at any given time. Voice coil motors of the prior art simply rely on each end of the armature travel as estimates of position. In a dynamic, ie. moving, system handling delicate parts which must be exactly located, this is not good enough. Overshoot at either end and intermediate positions must be known as well. In this case, voice coil motors of the prior art may rely on an independent, external measuring device, such as a linear voltage differential transformer (LVDT) or linear potentiometer, to provide accurate positional information. Of necessity, this adds bulk and mass to the essential moving part of the motor, the bobbin, and increases the difficulty of aligning the various components during assembly.
In view of the foregoing, it is therefore an object of the present invention to provide a voice coil motor suitable for handling semiconductor die.
Another object of the present invention is to provide an improved voice coil motor in which the force applied by the motor is controlled.
A further object of the present invention is to provide a voice coil motor having an armature which can be located accurately.
Another object of the present invention is to provide an improved voice coil motor wherein the velocity of the armature can be controlled accurately.
A further object of the present invention is to provide an improved voice coil motor suitable for use in industrial or dirty ambients.
Another object of the present invention is to provide an improved voice coil motor having a linear bearing for rigidly supporting the armature.